This invention discloses advanced solid-chemical compositions which provide balanced, sustained-release sources of soluble and insoluble organic substrates and complex inorganic phosphates, as well as other beneficial agents, which when used as intended, promote the bioremediation of contaminated environmental media. Specifically, the present invention was developed to provide a relatively simple and inexpensive means of enhancing the anaerobic bioremediation and dehalogenation of halogenated organic contaminants, such as trichloroethene (TCE), as well as the biologically mediated chemical reduction of oxidized forms of certain inorganic contaminants, such as chromium (VI), uranium (VI), and arsenate-based pesticides. Either alone or in combination with other liquid- and solid-chemical compositions, it is the inventor""s belief that the present invention also has the potential for the remediation of the gasoline additive methyl tertiary butyl ether (MTBE).
The disclosed solid-chemical compositions of the present invention provide improved means for (1) creating, enhancing, and maintaining anaerobic if not anoxic conditions by facilitating the biologically mediated removal of the available oxygen from the media; and (2) creating and maintaining reducing conditions (i.e., negative Eh values) and near neutral to slightly acidic pH conditions (6xe2x89xa6pHxe2x89xa68) which favor anaerobic, biologically mediated chemical-reduction reactions, e.g., the reductive dehalogenation of halogenated organic contaminants and the reduction of the oxidized forms of certain metals. The disclosed solid-chemical compositions also provide means for maintaining the aforementioned conditions for sufficiently long periods of time to enable the biologically mediated degradation, transformation, and/or detoxification reactions to proceed to the extent that the concentrations and/or toxicity of the contaminants are reduced to acceptable levels.
Soil and ground-water pollution caused by chemical contaminants released into the environment is a well documented, world-wide problem. Such chemical contamination is associated with many different types of industrial activities over the last two centuries. Common environmental contaminants include several different types and forms of petroleum hydrocarbons, halogenated organic compounds including solvents (e.g., tetra- and trichloroethene, methylene chloride), organochlorine pesticides (e.g., DDT and toxaphene), polychlorinated biphenyls (i.e., PCBs), and heavy metals and other inorganic contaminants such as cyanides. The available toxicological data indicates that many of these contaminants, in particular many of the halogenated organic compounds, are toxic, carcinogenic or potentially carcinogenic to humans, animals and other environmental receptors. In addition, the available environmental and ecological data have shown that many of these contaminants tend to persist in the environment for long time periods. The long-term stability and extremely slow degradation of many such environmental contaminants presents a substantial, long-term hazard to human health and the environment throughout the industrialized world.
Many of the so-called conventional methods for the remediation or clean-up of chemically contaminated wastes, waters, soils, and sediments have generally involved either the physical removal of the contaminated media or the simple mass transfer of the contaminants from one media (e.g., soil) to another (e.g., air). In general, such physical-treatment technologies do not involve the chemical and/or biological destruction, breakdown, transformation, or detoxification of the contaminants. Two of the most common categories of physical environmental-remediation technologies are the excavation and off-site disposal (or treatment) of contaminated soils and the pumping and subsequent treatment of contaminated ground water. The excavation of contaminated soils is often followed by their disposal in a landfill, which can pose a potential long-term risk to the environment, or their incineration, which may result in the release of air pollution. Many ground-water pump-and-treat processes involve the simple mass-transfer or xe2x80x9cstrippingxe2x80x9d of the contaminants from the water into the air. Another common physical-treatment method involves the use of granular activated carbon (GAC) reactors to treat chemically contaminated waters. When contaminated water is passed through a GAC reactor, the contaminants are physically adsorbed onto the carbon particles, thereby producing another contaminated media which requires subsequent disposal and/or treatment. Each of these physical-treatment technologies share the same disadvantagexe2x80x94they do not reduce the actual amount or toxicity of the chemical contaminants, but rather they simply move the contamination from one place to another or from one media to another.
Another category of environmental-remediation technologies, termed bioremediation, involves the use of microorganisms to convert chemical compounds into innocuous or less harmful chemical compounds. Bioremediation technologies generally have lower costs associated with their use and implementation than do the competing physical technologies. Bioremediation technologies can also be adapted to a broader range of contamination problems and variations in field conditions than other types of remediation technologies.
The most promising bioremediation technologies provide the additional capability of treating contaminated media in-situ, i.e., in place, without the need for ground-water pumping or soil excavation. Current trends in bioremediation technology indicate that the most technically feasible and commercially successful bioremediation technologies are those which promote bioremediation processes mediated by indigenous or xe2x80x9cnativexe2x80x9d contaminant-degrading bacteria, fungi and other microorganisms which are naturally present in the, contaminated media. The presence of naturally occurring, contaminant-degrading microorganisms in many different types of environmental media has been extensively documented in the scientific literature. There is an extensive body of prior-art literature and patents concerning various means of using both aerobic and anaerobic bioremediation processes, engineered bacteria, and the xe2x80x9cbioaugmentationxe2x80x9d of contaminated media with cultured microorganisms and fungi to promote the biodegradation of organic contaminants in water, soil, and industrial wastes. For example, it has been reported that native Alcaligenes spp., Pseudomonas spp., and Enterobacter spp. can degrade a number of pesticides and polychlorinated biphenyls (Nadeau et al., 1994, Applied and Environmental Microbiology; Aislabie et al., 1997, New Zealand Journal of Agricultural Research; Galli et al., 1992, Pseudomonas: Molecular Biology and Biotechnology). Recent trends in the art and literature acknowledge a growing understanding of the use of anaerobic biological processes in the treatment of many different types of contaminants that are otherwise recalcitrant under aerobic conditions. In particular, trends in the art reflect a growing understanding of the need and importance of achieving and maintaining anaerobic conditions and other factors which favor the biologically mediated chemical reduction, dehalogenation, biodegradation, transformation, and/or detoxification of recalcitrant organic and inorganic contaminants in the environment.
U.S. Pat. No. 6,066,772 to Hater et al. (to Waste Management, Inc. and International Technologies Corporation) discloses a two-step, biologically mediated process for converting hazardous explosives such as nitroaromatic and nitramine explosives in soil, resulting in soils free of explosive contaminants and their reduced derivatives. The anaerobic step involves mixing natural microorganisms and an oxidizable carbon source (e.g., dextrose, molasses, beet juice, potatoes, sweet potatoes, corn starch, potato starch) into the soil to produce reduced residues of the explosives. The second, aerobic step involves mixing the resultant reduced residues with a compostable material (e.g., grass clippings, yard waste, municipal solid waste, landfill compostable materials) and aerating via mechanical agitation or introduction of pressurized air. Hater et al. do not disclose the application of their process for the treatment of environmental media other than soil, nor do they disclose the application of their process to the remediation of contaminants other than explosives. Hater et al. do not disclose the formulation or use of solid-chemical compositions, such as those disclosed in the present invention, which provide for a sustained-release of soluble and insoluble substrates and complex inorganic phosphates. Hater et al. also do not disclose the application or use of additional nutrients or beneficial agents disclosed herein. Hence, Hater et al. do not disclose the present invention.
U.S. Pat. No. 5,062,956 to Lupton et al. discusses a method of reducing soluble Cr(VI) using fermentative, sulfate-reducing anaerobic bacteria to reduce Cr(VI) to Cr(III) and immobilize the latter as the extremely insoluble hydroxide which settles out as a solid. Carbon sources such as acetic acid, phosphoric acid, hydrochloric acid, sulfonic acid, carboxylic acids, molasses, lactic acid are cited which are disclosed to be used as microbial growth agents. Likewise, nutrients such as nitrogen, phosphorus, and trace elements may be added to support microbial growth if they are deficient in the system. Aqueous residues containing undesirable amounts of Cr(VI) are treated in a continuous bioreactor. Lupton et al. do not disclose the formulation or use of solid-chemical compositions, such as those disclosed in the present invention, which provide for a sustained-release of soluble and insoluble substrates and complex inorganic phosphates. Lupton et al. also do not disclose the application of their method for in-situ remediation, nor do they disclose the application of their process to contaminants other than metals. Hence, Lupton et al. do not disclose the present invention.
U.S. Pat. No. 5,681,739 to Turick et al. discloses a method of reducing the concentration of Cr(VI) in a liquid aqueous residue comprising the steps of providing anaerobic Cr(VI)-reducing bacteria, mixing the liquid aqueous residue with a nutrient medium (e.g., molasses, acetic acid, amino acids, casamino acids, urea), and contacting the mixture with the anaerobic bacteria to enhance the reduction of Cr(VI) to Cr(III). This process can be used for the bioremediation of hexavalent chromium contaminated soil and/or ground water that can be practiced in-situ, ex-situ, or both. The procedure is carried out in an ex-situ bioreactor or in-situ, using the earth as a bioreactor by stimulating indigenous bacteria by adding the nutrient medium directly to the environment. Turick et al. do not disclose the application of their method to contaminants other than metals. Turick et al. do not disclose the formulation or use of solid-chemical compositions, such as those of the present invention, which provide for a sustained-release of soluble and insoluble substrates and complex inorganic phosphates. Hence, Turick et al. do not disclose the present invention.
U.S. Pat. No. 5,582,627 to Yamashita discloses a composition for degrading organic contaminants in soil consisting of a nutrient medium serving as a substrate for microorganisms in the soil (e.g., molasses, mannose, lactose, dextrose, arythrose), a macronutrient component (e.g., ammonia; urea; ammonium salts; nitrates; amino acids; proteins; nucleic acids; phosphoric acid; single, double, and triple superphosphates; salts of phosphoric acid; nitric phosphates; pyrophosphates; nucleic acid phosphates), a micronutrient component (e.g., zinc, iron, manganese), a complexing agent (e.g., lignosulfonates, citric acid, humic acid), and a vitamin/co-factor component (e.g., thiamine, riboflavin, nicotinic acid, pyridoxine, folic acid). The composition is in the form of a liquid and may be applied to the soil through irrigation water or direct spraying onto the soil. Alternatively, the composition may be in the form of a dust or granular material that can be directly mixed into the soil or applied as a suspension in water. Yamashita does not disclose the application of the composition for the treatment of environmental media other than soil or for the treatment of inorganic contaminants. Yamashita does not disclose the formulation or use of solid-chemical compositions, such as those of the present invention, which provide for a sustained-release of soluble and insoluble substrates and complex inorganic phosphates. Hence, Yamashita does not disclose the present invention.
U.S. Pat. No. 5,968,359 to Krahn et al. discloses a method of cleaning up heavy metal-laden soils and water by creating conditions such that microorganisms will form hydrogen sulfide which reacts with heavy metals to form sulfides. According to Krahn et al., by creating hydrogen sulfide, it is possible according to the use of their invention to encapsulate and immobilize heavy metals in the pollution zone. To induce or accelerate the process, a biologically utilizable organic substance is added as a carbon source to ensure anaerobic conditions. Such carbon sources include molasses, acetates, lactates, glycerol, ethanol, and waste from sugar beet production and beer production. Yeast, inorganic nutrients, buffering salts, and sulfur sources are also added to the composition. Krahn et al. do not disclose the application of their method to contaminants other than metals. Krahn et al. do not disclose the formulation or use of solid-chemical compositions, such as those of the present invention, which provide for a sustained-release of soluble and insoluble substrates and complex inorganic phosphates. Hence, Krahn et al. do not disclose the present invention.
Suthersan (U.S. Pat. No. 5,554,290), Nyer and Suthersan (Ground-Water Monitoring Review (GWMR), Summer 1996), and Nyer et al. (GWMR, Spring 1998) teach an in-situ bioremediation process for the creation of what they term xe2x80x9cin-situ reactive zones.xe2x80x9d These reactive zones create an anaerobic environment in the aquifer through the injection of an easily biodegradable carbon source, such as molasses. The injection of molasses causes a rapid increase in the biological activity in the aquifer, thereby consuming the dissolved oxygen and other electron acceptors present in the ground water. A reducing environment is created, whereby Cr(VI) can be removed from solution and precipitated as a chromium hydroxide, nitrates can be anaerobically degraded, and/or chlorinated hydrocarbons can be dehalogenated. The biodegradable carbon source is applied as a dilute aqueous solution. Suthersan (U.S. Pat. No. 5,554,290), Nyer and Suthersan (GWMR, Summer 1996), and Nyer et al. (GWMR, Spring 1998) do not discuss the application of in-situ reactive zones to environmental media other than ground water, nor do they discuss the addition of nutrients to the aqueous solution to promote the growth of contaminant-degrading bacteria. Suthersan (U.S. Pat. No. 5,554,290), Nyer and Suthersan (GWMR, Summer 1996), and Nyer et al. (GWMR, Spring 1998) do not disclose the formulation or use of solid-chemical compositions, such as those of the present invention, which provide for a sustained-release of soluble and insoluble substrates and complex inorganic phosphates. Likewise, they do not disclose the application of the solid-chemical sources of carbon substrates in the preferred forms of granules, briquettes, pellets, tablets and the like. Hence, Suthersan (U.S. Pat. No. 5,554,290), Nyer and Suthersan (GWMR, Summer 1996), and Nyer et al. (GWMR, Spring 1998) do not disclose the present invention.
In accordance with the present invention, novel solid-chemical compositions are provided for promoting the anaerobic, biologically mediated chemical reduction, biodegradation, transformation, and detoxification of halogenated and hydrophobic organic contaminants and certain inorganic contaminants which may be present in solid and liquid wastes, soils, sediments, water bodies and other environmental media. The principles of this invention provide for a relatively simple and cost-effective means for promoting the anaerobic bioremediation and biologically mediated chemical reduction of such contaminants.
A further object of the invention is to present means by which to overcome the disadvantages associated with not only the traditional methods of remediation previously described but also the limitations of other more recent and/or technically advanced anaerobic bioremediation and chemical-reduction processes described in the prior art. The present invention also provides for significant cost savings relative to other means and methods for environmental remediation. Specifically, the present invention can reduce the operation and maintenance (OandM) costs associated with environmental remediation programs, and it can reduce, if not eliminate, the need for excavation, pumpage, transportation, and/or off-site treatment of contaminated wastes, soil, or water.
The purpose of the present invention is to disclose advanced solid-chemical compositions which provide for a sustained release of organic substrates and complex inorganic phosphates. Specifically, in addition to the complex inorganic phosphates, the solid-chemical compositions of the present invention provide a combination of both water-soluble and insoluble organic substrates, the combined effect of which is to provide both short-lived and long-lived sources of electron donors. Several other beneficial agents may also be included in the solid-chemical compositions of the present invention to enhance the forms and functions of the compositions. These compositions are designed to create, enhance, and maintain anaerobic and reducing conditions which favor anaerobic biodegradation and biologically mediated chemical-reduction processes, e.g., the reductive dehalogenation of halogenated organic contaminants and the reduction of the oxidized forms of inorganic species such as Cr(VI) and U(VI) by anaerobic microorganisms.
The discoveries disclosed herein indicate and/or strongly suggest that many recalcitrant environmental contaminants can be effectively degraded, transformed, and/or detoxifield by indigenous, contaminant-degrading bacteria when the solid-chemical compositions disclosed herein are applied to the contaminated media and the media are subsequently maintained under conditions favorable to the anaerobic microorganisms and the biogeochemical reactions mediated by these organisms, i.e., the media are kept moist or nearly saturated with water These and other objects and advantages of the present invention will become apparent to those skilled in the art following the detailed description of the invention which reveals the novel combination of solid chemical compositions described herein, and more particularly as defined by the claims.